In a current model of the peripheral primate visual system, phasic neurons transmit information about achromatic brightness and border contrast as well as temporal luminance changes; tonic neurons transmit information about color (hue, saturation, and temporal color changes) and about achromatic border contrast. Results presently in the literature suggest an alternate hypothesis: Perception of spatial contours (borders), brightness, and color is determined exclusively by the tonic system. The sole function of the phasic system is the perception of temporal luminance changes; it does not participate in either brightness or spatial vision. It is proposed to further test and develop this model with a series of psychophysical experiments designed to isolate the tonic and phasic systems. Tonic and phasic responses will be distinguished by the selective adaptation and selective sensitivity of each system to specific stimulus parameters.